The rhizosphere is the zone of soil surrounding plant roots that is under the influence of the root. Microbes in the rhizosphere, such as beneficial biocontrol bacteria, provide essential services for plant hosts. The primary weakness of conventional technologies that deliver bacteria to roots is the failure to deliver enough functional bacteria to the critical locations within the rhizosphere. Beneficial bacteria added in seed coatings often fail to survive and proliferate and/or fail to colonize growing roots. Spatial investigations of beneficial bacteria along roots have shown many empty patches and reduced abundance of beneficial bacteria with distance from seed to root tip. Furthermore, even if biocontrol bacteria do attach to an emerging root, seedling roots grow very quickly from the leading edge, such that beneficial bacteria cannot reproduce fast enough and become dilute at the growing root tip. Thus, improved compositions and methods are needed for delivering beneficial bacteria and other agricultural payloads to vulnerable roots in actively-growing plants.